Push button arrays have been increasingly employed in vehicle control panels as an interface between the operator and a vehicle system, such as a climate control system. Legends and symbols formed on the face of the various buttons are preferably illuminated from behind, or back-lit, for convenient operation under low-ambient lighting conditions. To minimize cost and heating, multiple buttons are typically illuminated with a single lightpipe passing through the array behind the button faces.
In order to increase the number of buttons in a given area, or to group the buttons for function differentiation, it may be desired to space the buttons very closely. In conventional push button arrays however, a spacing limitation arises due to the use of a light-trapping wall formed between adjacent buttons. This is best illustrated in reference to FIG. 1, which depicts a conventional serial array of three push buttons 10, 12 and 14. The buttons 10-14 are assembled into individual cavities formed in a molded housing defined by an outer shell 16 and one or more compartment walls 18, and are supported for limited axial movement therein. The face 20 of each respective button 10-14 protrudes through an aperture in the outboard face 22 of the cavity, outboard movement of the buttons 10-14 being limited by engagement of laterally and longitudinally extending button surfaces 24 with complementary flanges 26 formed on the outer shell 16 and compartment walls 18.
The buttons 10-14 are retained in the housing by a switch array comprising a circuit board 28 and an elastomeric membrane 30. The membrane 30 defines a raised dome 32 which contacts the inboard end of each button 10-14, resiliently urging the buttons 10-14 to their outboard travel limits. The circuit board 28 carries a pair of conductive paths 34 under each dome 32, and a conductive pad 36 in the center of each dome 32 is provided to engage and bridge the conductive paths 34 when the respective button 10-14 is depressed.
A stationary elongated lightpipe 38 adapted to be illuminated by a lamp 40 passes through the buttons 10-14 and compartment walls 18, illuminating the interior of each button 10-14 when the lamp 40 is lit. The face of each button 10-14 is generally opaque except for a translucent area (not shown) defining a symbol or legend to be illuminated in low ambient conditions. When the lamp 40 is lit, light from the lightpipe 38 shines through the translucent areas on the faces of the buttons 10-14, illuminating the symbols and legends for convenient viewing by the operator of the vehicle.
During low ambient conditions when the lamp 40 is lit, the lateral overlap between the button surfaces 24 and the housing flanges 26 operates to prevent light from shining through the area between adjacent buttons. Generally, an overlap of at least 1.0 mm is required. This overlap limits how closely the butlons 10-14 may be spaced. Referring to FIG. 1, for example, it will be seen that the buttons 10-14 may be spaced no closer that approximately three times the required flange overlap, or about 3.0 mm.
One known technique for addressing the above-described limitation without actually changing the spacing of the buttons is to laterally extend the outboard faces of the buttons, giving the appearance of close spacing. However, this does not increase the number of buttons that can be placed in a given area, and further, the legends or symbols can only be deployed in the center of the button.